I get the impression from reading these posts that leasing modern trains especially the way SWT do has put a whole extra layer of quite significant costs in the system and ultimately the old fashion way of simply buying trains will ultimately be found to prove to be the best value ,like that saying "The best ideas are often the simplest"
I think the main problem with that is that modern trains are expensive, and so for a TOC like SWT, to replace a large fleet of slam-doors by buying even more expensive desiros, would probably cost most of their income for their contractual period. Imagine if stagecoach spent billions of pounds on a new fleet, only to be told after 5 years "Sorry but your time is up. First group are now going to have a go at running the franchise" They would either:
a) sell first group their fleet of desiros for the same amount or even more than they bought them for (bankrupting first group)
b) Move their fleet of desiros to another one of their franchises (unlikely, unless 3rd rail springs up around nottingham)
c) Be made to surrender their trains to first group by the government, loosing their billions of pounds of investment instantly.
In order for that to work, you'd need to have long term contracts (about the lifetime of the stock!)